True blue

Australian Geographic - - Wild Australia - JOHN PICKRELL is a for­mer AUS­TRALIAN GEO­GRAPHIC edi­tor. Fol­low him on Twit­ter: @john_pick­rell

Ever won­dered why the blue­tongue lizard’s tongue is such an un­usual hue?

YOU’VE prob­a­bly ex­pe­ri­enced it your­self on a bushwalk – a star­tled blue­tongue skink ex­poses its large blue tongue, of­ten si­mul­ta­ne­ously hiss­ing and in­flat­ing its body to look big­ger and more threat­en­ing. Blue­tongue skinks of a num­ber of species are medium-sized, ground-dwelling lizards that are com­monly found across Aus­tralia and New Guinea.They have become pop­u­lar pets in Aus­tralia and around the world.

The blue­tongue’s tac­tic may seem fa­mil­iar to Aus­tralians, but this is an un­usual be­hav­iour and dis­play for a lizard. And although it has long been as­sumed that this is a strat­egy for avoid­ing preda­tors, no­body has tested the idea sci­en­tif­i­cally, un­til now.

Now re­searchers, in­clud­ing Dr Martin Whit­ing of Mac­quarie Univer­sity in Syd­ney, have shown that, at least in the north­ern blue­tongue skink ( Tili­qua scin­coides in­ter­me­dia), the dis­play is part of a last-ditch de­fence mech­a­nism that these rep­tiles use to save them­selves from being eaten, par­tic­u­larly from bird preda­tors.

It is, Martin says, so-called deimatic be­hav­iour – a very fast dis­play that is over quickly and highly con­spic­u­ous. These kinds of dis­plays are in­tended to in­duce a star­tle re­sponse in a preda­tor, such as an ea­gle or a hawk, over­load­ing its senses and caus­ing it to pause, slow or stop its at­tack. Aus­tralia’s frill-neck lizard is an­other rep­tile that uses this kind of strat­egy to avoid be­com­ing prey.

“We sus­pect that such a highly con­spic­u­ous dis­play de­ployed at close range to a preda­tor will in­duce a re­flex­ive star­tle re­sponse that will de­ter preda­tors,” the au­thors re­port in the May edi­tion of the jour­nal Be­hav­ioral Ecol­ogy and So­cio­bi­ol­ogy. “We also hy­poth­e­sise that this type of dis­play will be par­tic­u­larly ef­fec­tive against aerial preda­tors, for which an in­ter­rupted at­tack would not be eas­ily re­sumed due to loss of in­er­tia.”

“The lizards re­strict the use of full-tongue dis­plays to the fi­nal stages of a pre­da­tion se­quence when they are most at risk, and do so in con­cert with ag­gres­sive de­fen­sive be­hav­iours that am­plify the dis­play,” says lead au­thor Ar­naud Ba­di­ane, also of Mac­quarie Univer­sity.

The sci­en­tists made their dis­cov­ery af­ter taking 13 north­ern blue­tongue skinks – the largest blue­tongue species – and com­par­ing the colour and in­ten­sity of dif­fer­ent re­gions of their tongues. By us­ing a de­vice called an op­tic spec­trom­e­ter to look at the tongues of skinks held in an out­door en­clo­sure near Ku­nunurra, in the Kim­ber­ley,Western Aus­tralia, they dis­cov­ered that the lizards’ tongues brightly re­flected UV light.This is highly vis­i­ble to preda­tors such as birds, goan­nas and snakes.The in­ten­sity of the UV colour was found to be much greater at the back of the tongue than the front.

The re­searchers then sim­u­lated at­tacks to show that the skinks at­tempted to re­main cam­ou­flaged – taking ad­van­tage of their brown stripy body coloura­tion – un­til the very last mo­ment, when they opened their mouths wide to ex­pose their tongues, flat­ten­ing and ex­pand­ing them.

The tests showed that the greater the in­ten­sity of the at­tack, and there­fore the risk that the skinks per­ceived, the greater the ex­tent of the “full­tongue dis­play”, with more of the bright UV back of the tongue ex­posed. These full-tongue dis­plays were strong­est in re­sponse to sim­u­lated bird and fox at­tacks, rather than those meant to mimic snakes and goan­nas.

“The tim­ing of their tongue dis­play is cru­cial,” Ar­naud says. “If per­formed too early, a dis­play may break the lizard’s cam­ou­flage and at­tract un­wanted at­ten­tion by preda­tors and in­crease pre­da­tion risk. If per­formed too late, it may not de­ter preda­tors.”

So, next time you star­tle a bluey while you’re out for a bushwalk, you’ll know just why it’s

be­hav­ing the way that it does!

It seems shock is ex­actly the re­sponse Aus­tralian blue­tongue skinks are look­ing for when they flash their vivid tongues.

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